In order to realize an electrical or an electronic circuit, passive components are required besides active components, such as e.g. transistors. One of the most important passive components, besides resistors and capacitors, is a coil. A coil generally consists of wound or spiral conductor loops. The properties, for example the inductance, of the coil are usually crucially dependent on the materials used, the number of turns (coil turns, coil windings) and the physical dimensions, such as the diameter of the conductor, the size of the coil, etc. A coil is often used in a frequency-determined or -determining circuit such as e.g. an oscillator or a filter, and in a circuit for current smoothing or in a power supply unit. In a radio-frequency/broadband amplifier circuit, a coil is predominantly employed for improving the amplifier characteristic, i.e. for increasing the bandwidth and/or for smoothing the amplitude response, and for improving the input/output matching.
In the course of miniaturization and in present-day microelectronics, the electronic components are integrated by semiconductor technology and form a chip, which in turn constitutes a complex electronic component having a new function. In this case, the individual elements of the microelectronic circuits are produced on a semiconductor substrate, the so-called wafer, by corresponding doping/alloying and by targeted application of functional metal layers (also referred to hereinafter as metal plies or metal planes or metallization planes or metallization layers). This gives rise to a structure of a plurality of horizontal metal layers (also referred to as a metal stack, which is dependent on the respective technology specification) which are electrically insulated from one another and can be connected to one another by vias (known as vertical interconnect access, vias; also referred to hereinafter as contact feedthroughs, interlevel connection); in a manner similar to that in the case of a multilayered printed circuit board. The designation of the orientation as horizontal is defined here by the plane/position of the semiconductor substrate. The individual metal plies are thus arranged parallel to one another and parallel to the substrate; that is to say are situated in the horizontal plane. A vertical orientation thus designates a plane which is situated perpendicularly to the substrate and to the individual metal plies.
If a coil is integrated in such a semiconductor technology, then this is usually done nowadays on a horizontal metal plane by conductor tracks with a specific width being arranged in a spiral fashion. As a result of this horizontal arrangement, the coil occupies a very large area and not uncommonly is larger than the remaining part of the circuit. Since the costs in the semiconductor industry are calculated with regard to the chip area used, the coil thus constitutes the largest cost factor in such a circuit.
Hitherto a coil and thus the coil turns have been integrated in the horizontal plane of a chip [Chen, J. & Liou, J. J., On-Chip Spiral Inductors for RF Applications: An overview, J. Semiconductor Techn. Sci. 4, 149 (2004)]. For this purpose, a metallic strip conductor having a specific width is arranged in a spiral fashion on a metal ply in the metal stack. This is carried out on one of the upper metal plies of the metal stack. One connection of the coil is then led from the outer edge of the conductor strip spiral as connection toward the outside. Since strip conductors are not permitted to cross one another on the metal ply, the second connection of the coil is led from the interior of the spiral by way of a via to a higher or lower metal ply in the metal stack and the connection is established from there.
Furthermore, there are also coils which, although referred to as vertical coils, do not exclusively use the vertical plane or lie in a planar fashion in the vertical plane. Rather, although in such an arrangement the strip conductor is led from one metal plane to the next, the actual coil turns lie in the horizontal plane, as a result of which the coil region defined by the coil turns lies in the horizontal plane and thus parallel to the main processing surface of the substrate. This gives rise for example to a coil in the form of a cylindrical coil [Tsui, H.-Y. et. Al., An On-Chip Vertical Solenoid Inductor Design for Multigigahertz CMOS RFIC, IEE Transactions on Microwave Theory and Technique 53, 1883 (2005)]. Furthermore, coils can be connected to one another or cascaded with one another. These arrangements are known as stacked integrated coils [Yousef, K. et al., Design of 3D Integrated Inductors for RFICs, Japan-Egypt Conf. on Electronics, Communications and Computers (JEC-ECC), 22 (2012)]. Furthermore, there are helical arrangements in which individual vertical conductor loops are horizontally connected to one another [US 2012/0268229 A1].